Why is the order of magnitude of

5x10^-11

-10 instead of -11?

3 answers

In a relative sense, 5*10^-11 is closer to 10^-10 than 10^-11, even though it is the arithmetic mean of the two. When talking about orders of magnitude, think logarithmically.
can you elaborate on the lograithmically bit u mentioned?
On a log scale, orders of magnitude (factors of ten) are equally spaced.
Log 1 = 0
Log 5 = 0.699
Log 10 = 1
Log 100 = 2
etc.
That is why 5 is "closer" to 10 than 1. logarithmically speaking?